A drawback with engines used at present is that some of the gases already burned during the preceding power stroke remain in the cylinder space, which is liable to impair efficiency since there is no combustion of gases already burned. Furthermore, during the flushing of a cylinder space, some of the fuel-and-air mixture may find its way into the exhaust manifold which causes an increase in the consumption of fuel.
One solution for improving the operation of an internal combustion engine is disclosed in the publication DE-OS 19 20 751. This publication describes an apparatus for preventing the passage of fuel-and-air mixture through the outlet valve into the outlet duct during an induction stroke. The apparatus includes an air pipe, which is fitted in the intake manifold and from which branches an air duct to the base of each inlet valve. The air issuing from this air duct provides a flushing effect as the inlet valve and outlet valve are simultaneously open. However, the apparatus disclosed in the above publication is constructionally unreliable in providing a satisfactory flushing action. In addition, the cited publication does not take into consideration all possiblities for the operation of an engine achieved by means of air filling or the like.
The following is a list of the most essential features in terms of the operation of an engine for the passage of fuel-air-air-mixture:
The burned gases must be removed as thoroughly as possible from the cylinder space prior to passing a fuel-and-air mixture into the cylinder space
during the flushing no fuel-and-air mixture can be allowed to pass into the exhaust pipe,
filling of the cylinder space must be as complete as possible regardless of the running speed,
the simultaneous open condition or overlap results in increased filling and thus increased power,
cooling of the valves and cylinders by means of air increases the filling. In theory, this can be derived from the equation EQU .DELTA.V=.delta..multidot.V.sub.0 .multidot..DELTA.t
In the equation, V.sub.0 is the volume of gas at 0.degree. C. and the magnitude of coefficient .delta. is 1/273.degree. C..sup.-1. This leads to a conclusion that, when heated to 273.degree. C., the volume of gas expands to double, and
the complete combustion of fuel with excess air produces cleaner exhaust gases. This decreases especially the amount of the oxides of nitrogen.